A broadcast service provider transmits audio-video streams to a viewer's television. Interactive television systems are capable of displaying text and graphic images in addition to typical audio-video programs. They can also provide a number of services, such as commerce via the television, and other interactive applications to viewers. The interactive television signal can include an interactive portion consisting of application code, data, and signaling information, in addition to audio-video portions. The broadcast service provider can combine any or all of this information into a single signal or several signals for transmission to a receiver connected to the viewer's television or the provider can include only a subset of the information, possibly with resource locators. Such resource locators can be used to indicate alternative sources of interactive and/or audio-video information. For example, the resource locator could take the form of a world wide web universal resource locator (URL).
The television signal is generally compressed prior to transmission and transmitted through typical broadcast media such as cable television (CATV) lines or direct satellite transmission systems. Information referenced by resource locators may be obtained over different media, for example, through an always-on return channel, such as a DOCSIS modem.
A set top box connected to the television controls the interactive functionality of the television. The set top box receives the signal transmitted by the broadcast service provider, separates the interactive portion from the audio-video portion, and decompresses the respective portions of the signal. The set top box uses interactive information to execute an application while the audio-video information is transmitted to the television. Set top boxes typically include only a limited amount of memory. While this memory is sufficient to execute interactive applications, it is typically not adequate to store the applications for an indefinite period of time. Further, the memory of the set top box is typically too small to accommodate a program which includes large amounts of audio or video data, application code, or other information. Storage devices may be coupled to the set top box to provide additional memory for the storage of video and audio broadcast content.
Interactive content such as application code or information relating to television programs is typically broadcast in a repeating format. The pieces of information broadcast in this manner form what is referred to as a “carousel”. Repeating transmission of objects in a carousel allows the reception of those objects by a receiver without requiring a return path from the receivers to the server. If a receiver needs a particular piece of information, it can simply wait until the next time that piece of information is broadcast, and then extract the information from the broadcast stream. If the information were not cyclically broadcast, the receiver would have to transmit a request for the information to the server, thus requiring a return path. If a user is initially not interested in the carousel content, but later expresses an interest, the information can be obtained the next time the carousel is broadcast. Since broadcast networks have access only to a limited bandwidth, audio-video content is not broadcast in carousels. There is also insufficient bandwidth and server resources to handle pulling of large amounts of data required for video and audio in real-time to handle near simultaneous requests for broadcast of previously broadcast material from a vast number of television viewers.
In a broadcast by a television network, such as a broadcast of a sporting event, the content provider may generate multiple video feeds from various angles of the game, for example. The network may select one or more feeds from the multiple video feeds and broadcast the selected video feed(s) to the viewing audience at any given point in time. That is, the network may simultaneously broadcast video tracks that present the same scene, except from a different perspective or send different audio tracks or subtitles if a movie is broadcast in different languages, for example. The viewer may use an interactive application that executes on their set top box to choose between different perspectives. When a viewer requests a change in perspective, the interactive application uses meta-data to determine which packets contain the chosen perspective. It starts delivering packets that contain the newly chosen perspective.
As previously described, a viewer cannot request previously broadcast audio or video material due to the limited bandwidth available on broadcast networks. Also, data that accompanies interactive applications sometimes corresponds to audio and video that is currently being broadcast, so it changes frequently. In these cases, the values broadcast as part of the carousel often change and old values are no longer carried in the carousel. Thus, a viewer cannot replay a scene or a sporting event play from a different perspective unless the viewer has already recorded the video stream for the alternate perspective.